Enhanced visible light degradation of indigo carmine dye using conventional and green synthesized TiO2 conjugates with porphyrin

• 5,10,15,20-tetrakis(4-carboxyphenylporphyrin) (P) is effectively adsorbed on TiO 2 nanoparticles. • P effectively enhances the absorbance of TiO 2 in the visible range of the spectrum. • Incorporation of indium(III) enhances the intersystem crossing, singlet oxygen quantum yield and photocatalytic activity of the conjugates against indigo carmine dye. • Green synthesized nanoparticles from orange peel extract show better photocatalytic activity against indigo carmine dye than conventionally synthesized nanoparticles. Photocatalysis utilizing TiO 2 nanoparticle semiconductors has emerged as a promising robust and cost-effective promising strategy for degradation of organic pollutants in wastewater. Herein, the application of visible-light-driven degradation of indigo carmine dye in aqueous media using TiO 2 -porphyrin conjugates is reported. TiO 2 nanoparticles were synthesized via conventional and green synthesis while the conjugates were synthesized via adsorption method, combining TiO 2 nanoparticles with porphyrin molecules. Various characterization techniques were employed, including XRD, FTIR, EDX, SEM, TEM, DLS, BET, TGA, UV-Vis spectrophotometry, fluorescence spectroscopy, and TCSPC. While FTIR confirmed the successful attachment of porphyrin molecules to the TiO 2 surface, XRD revealed that porphyrin had minimal effect on the anatase phase of the TiO 2 nanoparticles. The UV–Vis spectra showed a 10 nm red-shifted absorbance of InP and enhanced visible light absorbance by the conjugates. Although TiO 2 decreased the singlet oxygen quantum yield from 0.74 to 0.84 for P and InP to 0.59, 0.55 and 0.54 for P-T1, P-T2, and P-T3, respectively the heavy atom effect was observed, increasing Φ Δ to 0.73 for InP-T1. However, the highest photocatalytic degradation was achieved with T2-InP which degraded up to 99.73 % of indigo carmine under visible light after 120 min, showcasing the importance of metalation as well as green synthesis in the design of porphyrin-TiO 2 conjugates in photocatalysis.